The present invention relates to a new and improved construction of apparatus for rotating a multiply-mounted shafting, which is of the type comprising a rotational or rotative device for the continuous rotation of the shafting at a first rotational speed and an auxiliary rotational or rotative device for the continuous or intermittent rotation of the shafting at a second rotational speed which is lower in comparison to the first rotational speed.
At different stages during the operation of a thermal turbo-machine there can arise different disturbances, usually caused by thermal conditions. An internal secondary flow extending in the peripheral-and/or lengthwise direction of the rotor can lead to irregular heating or cooling of the rotor periphery and can result in warping or distortion of the rotor. The same secondary flow, in addition to different insulation losses arising in the casing or housing, causes distortion of such casing or housing. The distortion of the rotor and casing, in extreme cases, can result in scraping of the blades or buckets, i.e. in contact with the sealing portions and can even totally prevent any further rotation of the rotor. Even slight distortion of the rotor can result in impermissible vibrations due to imbalance upon restarting of the machine. In order to avoid these disturbances it is conventional practice to rotate the rotors continuously or intermittently, at rotational speeds which are advantageously pre-selected in consideration of the different operating stages and the momentary prevailing conditions.
During operation of a steam turbine installation there arise a number of so-called "critical periods", which require undertaking measures in the interest of providing the requisite operational safety and operational preparedness. Prior to start of the turbine there is initially placed into operation the steam generator, the vapor is condensed in the condenser and the labyrinth seals of the rotor are blocked with moderately hot vapor. In order to avoid impermissible distortion of the rotors such are rotated, as a function of their slimness and the temperature distribution, at such rapidity that there does not occur any scraping of the rotor-sealing parts or other critical locations; and for instance one-half of a revolution (180.degree.) carried out intermittently each half hour is sufficient for this purpose.
Upon start of the steam turbine assembly the residual distortion however is still so great that during running-up and passing through the resonance locations there occurs scraping. This residual distortion can be avoided by remaining over a longer period of time at lower starting rotational speeds, since in this way there is accomplished temperature equalization at the periphery of the rotor and there is eliminated rotor distortion. Such prolongation of the starting period is, however, undesired and it can be avoided by preliminary rotation of the rotor drive shafting at a minimum rotational speed of, for instance, 1 revolution per minute.
In the case of large steam turbines of 100 to 2000 MW containing two- or four-pole generators the rotor drive shafting is rotated at higher rotational speeds, between approximately 5 and 50 revolutions per minute or even greater, so that a hydrodynamic lubricant film is formed in the sliding or friction bearings, and there is thus avoided or reduced the wear of the bearings at the mixed friction zone.
Also the rotor of a generator can distort prior to start of the equipment, for instance when it must be energized, whether such be for pre-heating the windings and the rotor body or for synchronization of the generators of cross-compound assemblies prior to start-up, especially with low excitation current.
Too rapid rotation of the rotor shafting can be, however, disadvantageous in a number of respects. Thus, for instance, the prongs or points of the pine tree-like or serrated base of the buckets may be subject to impermissibly rapid wear, since the buckets, during each revolution, tend to vibrate or shake back and forth tangentially in their groove. If the bearing is equipped with high pressure lubrication in order to effectively reduce the friction during start of the shafting, then it can happen that due to the effects of dirt particles the shaft and the bearing metal are scratched and the high pressure lubrication and the oil wedge lubrication are ineffective at, for instance, 50 revolutions per minute. The consequence of this is slow wear of the bearings with attendant formation of a larger "support area" and an increase in play. This can be reduced by slower rotation.
Therefore, it is conventional to equip an installation of the aforementioned type with two devices for the rotation of the shafting. One of these is the standard rotational or rotative device which rotates the shafting at a rotational speed in the order of between 5 and 50 revolutions per minute so rapidly that there is insured for a so-called "vacuum drawing" with the attendant sealing of the labyrinths and subsequent running-up of the equipment in the shortest possible time without scraping and danger of scraping due to mechanically impermissible vibrations.
The other rotational device is an auxiliary rotational device which, as is usual, is arranged at one end of the shafting and generally comprises an intermittently rotating pawl device, however, also can be constituted by a continuously rotating device, operating at a rotational speed in the order of between 1 and 60 revolutions per hour, which is only rotated so rapidly that there is avoided a scraping at lower rotational speeds. If necessary, it can also be employed for overcoming the static friction, i.e. for starting the shafting, whereafter the standard rotational device then assumes rotation of the equipment.
Although the conventional auxiliary rotational devices fulfill their function quite well for many fields of application, there are however instances where the resistance-rotational moment is too great due to some type of disturbance in order to successfully overcome this condition by means of the auxiliary rotational device. Additionally, such arrangement is devoid of means which adequately informs the operator about the nature of an existing disturbance, so that the operator can decide whether and how the shafting should be rotated. This is especially disadvantageous in the case of nuclear power plants of the boiling water reactor type, since in such case the vapor is easily radioactive, and the shafting, the bearings, the rotational device and the auxiliary rotational device are only accessible with difficulty during operation to the plant personnel.